The present invention relates to a cryotherapy method for reducing tissue injury after balloon angioplasty or stent implantation. One of the well known and well documented causes of failure of angioplasty (use of a balloon inflated within an artery to compress occluding materials against the inner arterial wall) or stent implantation is the mechanism of restenosis. Restenosis is evidenced when the artery re-occludes due to tissue ingrowth and/or elastic recoil of the arterial wall at the site of the prior occlusion.
After a balloon angioplasty procedure or stent implantation procedure has been completed, the arterial wall often exhibits damage or inflammation due to the required use of force from inflation of a balloon catheter against the cellular layers of the arterial wall. This ingrowth phenomenon, namely, restenosis, affects the long term success of balloon angioplasties and stent implantations. In the prior art, cryotherapy is a known technique for preserving tissues at reduced temperatures for short periods of time. Cryotherapy has been decisively shown to be effective in tissue preservations maintenance of tissue function and facilitation of tissue healing processes. Some of the well-defined applications of cryotherapy include the following:
(1) Tissues collected from bovine, pigs and sheep are preserved at reduced temperature so that the elastic membranes or elastin present in the tissues is protected for subsequent applications. Without the use of such temperature reduction, the tissues dry out and lose their original mechanicals, physical and chemical properties.
(2) During open heart surgery, when the heart is opened to either replace a valve or an underlying diseased coronary artery, the myocardium or the tissues surrounding the heart are exposed to reduced temperature by dipping them in ice or sub-cooled water while the surgery is underway to preserve them.
(3) During open heart surgery, when the aorta is cross-clamped and blood from the heart is directed into a heart-lung machine, the blood is mixed with cold cardioplegia solution to preserve the cells and other essential components in the blood, an especially critical procedure where surgery is lengthy.
(4) Bovine and other homograft valves that have been preserved in cryo-based solutions and reduced temperature environment have been shown to have superior performance during long term follow-up studies when compared with mechanical bileaflet or single leaflet valves.
(5) In many pain management therapeutic situations, the area or region of acute pain is exposed to reduced temperature fluids or "cold packs" to reduce nerve damage and relieve pain.
The prior art teaches several techniques designed to reduce or eliminate the onset of restenosis. However, Applicant is unaware of any such technique that involves the use of application of reduced temperature within an artery.
One of the most common causes of recurrence of luminal narrowing after balloon angioplasty or stent implantation is the ingrowth of tissue at the site of the previous blockage. When a balloon is inflated at the site of a lesion where the artery is occluded, the lesion is mechanically pushed up by force acting thereon due to inflation of the balloon. Pathology of experiments in pigs and sheep reveals that the balloon inflation causes endothelial injury as well as tissue dislodgement at the site of the lesion. Such an injury is characterized by inner lumen wall cracks that are filled up with blood and some thrombis (clotting material). These cracks may infiltrate into the second and third layers of the vessel wall that are termed adventitia and media primarily composed of collagen, smooth muscle cells and elastic cells that contribute to the compliance of the artery.
When these layers are disrupted due to balloon inflation or stent implantation, compliance response is lost. This results in proliferation of cells as a function of time. Although the proliferation starts immediately after the injury to the arterial wall, maximum proliferation may be observed 6 to 18 months after the initial injury.
Applicant is aware of the following prior art:
U.S. Pat. No. 5,059,166 to Fischell et al. discloses a technique for reducing the onset of intimal hyperplasia which technique involves the use of irradiation from a radioisotope.
U.S. Pat. No. 5,213,561 to Weinstein et al. also discloses the use of radioactive material to reduce the incidence of restenosis.
U.S. Pat. No. 5,092,841 to Spears discloses the bonding of a bioprotective material to the arterial wall where angioplasty has been conducted.
U.S. Pat. No. 5,140,012 to McGovern et al. discloses a method for preventing onset of restenosis after angioplasty which involves administration of pravastatin in combination with an ACE inhibitor.
U.S. Pat. No. 5,242,397 to Barath et al. discloses prevention or reduction of the incidence of late restenosis through the administration of protein kinase C and tyrosine protein kinase inhibitors.
U.S. Pat. No. 5,284,869 to Bisaccia et al. discloses a method for preventing restenosis following angioplasty that includes the use of a photophoresis treatment method.
U.S. Pat. No. 5,298,018 to Narciso, Jr. discloses administration of a photosensitizer prior to surgical or interventional procedure which is then re-administered after the procedure to maintain the photosensitizer concentration level in the atheromatous plaque and smooth muscle cells in the vicinity of the lesion for a period of about 5-18 days.
U.S. Pat. No. 5,422,362 to Vincent et al. discloses administration of a green porphyrin to the location of vascular intervention to inhibit the onset of restenosis.
None of the patents discussed above teaches, discloses or suggests the use of a cryo-technique to reduce the onset of restenosis after a balloon angioplasty or stent implantation.
Further, Applicant is aware of an article titled "THE ROLE OF CRYOTHERAPY FOR AIRWAY COMPLICATIONS AFTER LUNG AND HEART-LUNG TRANSPLANTATION" by Maiwand et al. The article discusses the use of cryotherapy in causing cell lysis of granulation tissue and speculates that such a technique may therefore be effective after lung transplantation for difficult airway problems. This article fails to teach or suggest the use of cryotherapy techniques for reduction of the onset of restenosis within the arterial wall of a patient on whom balloon angioplasty or stent implantation has been completed.